Older donors have fewer influenza-responsive T cells prior to vaccination and a higher proportion of these T cells are of a late effector phenotype than those in younger donors.

<p>PR8-stimulated T cells were phenotyped for memory and effector T cell markers CD45RA, CD28, and CD27 in young, under 40 and older, 65+ donors. CD8 T cells were also examined for granzyme B expression after stimulation (flow cytometry gating as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023698#pone-0023698-g001" target="_blank">Figure 1</a>). (A) Proportions of influenza functionally responsive CD8 (<i>left</i>) and CD4 (<i>right</i>) T cells out of total CD8 and CD4 pools. (B) Division of influenza responsive CD8 and CD4 T cells into CD45RA⁻ memory and CD45RA⁺ late effector cell subsets. (C) Costimulatory molecule expression profiles in young and older donors in influenza responsive CD8 and CD4 T cells. (D) Granzyme B expression within the influenza responsive IFNγ⁺ CD8 T cell subset (<i>left</i>) and overall proportions of granzyme B⁺IFNγ⁺ CD8 T cells out of the total CD8 T cell population (<i>right</i>).</p>